Soybean glue



Patented Sept. 30, 1952 SOYBEAN GLUE Alexander J. Golick, Seattle, Wash., assignor to Monsanto Chemical Company, St. Louis, Mm, a, corporation of Delaware No Drawing. Ap licationruiyfza 1 949,

Serial No. ,500.

4. Claims. (Cl. 106-154) This invention relates to. an im rovement. in the wet mixing of, soybean glues and to the resulting adhesive. In particular, it discloses. a more stable plywood glue obtained by.- an initial heat treatment of the glue base in the presence of water prior to the addition of the strongly alkaline reagent chemicals required to make the final glue.

The general purpose of the invention is to greatly prolong the useful life; of the glue so as to prevent the losses and disadvantages-which have attendedthe objectionably rapid decomposition of soybean glues used hitherto. The presentprocess is broadly applicable to alkaline soybean glues in general and-its use is not restricted to any particular reagent formulation.

The soybean glues currently in, use for the manufacture of plywoodand the like are strongly alkaline colloidal aqueous dispersions; obtained by first mixing the soybean material as aheavy bodied suspension in a moderate amount of water to stir out lumps and thoroughly moisten and swell the particles, followed. by the. addition of further water to insure the. desired. final: con.- sistency along with strong alkalies including hydrated lime, caustic. soda, and. silicate of. soda, usually followed by carbon bisulfide. The final pH always is well abovepH' 11.5; The final water content of these glues generally ranges: between 3 and 4 pounds of water for. each pound? of original soybean glue base and, the desirable viscosity range is usually between about 25 and 150' as measured by the well known MacMicha'el'viscosity determining apparatus using; the No. 26 wire. The viscosity of such glues, however; does not remain constant but tends to increase" slowly for several hours and then decrease; The decrease in viscosity is attributed to some" form of protein decomposition indicated by the fact that. while no ammonia is added as a reagent inmaking the glue and the-odor-ofamm'onia is absent during the period in which the glue is slowly increasing in viscosity, nevertheless an ammoniacal odor becomes progressively evident during the period when the viscosity'is decreasing. It is also the experience of the industry that, after" any substantial decrease-in viscosity and particularly when the odor of. ammoniahas become evident, the adhesive properties of the; glue; are greatly diminished and will shortly disappear; Thus,

I originally normally thick glue, which hasthinned with age or developed an ammoniacal odor, has been found to have little: or no. adhesive power and is worthless.

The rate at which glues of-this: character decompose varies with time; and: temperature; der

. 2 teriorating most rapidly when mixed with warm water or in a warm room. In'any case, 'glue which has stood overnight is found to have lost either a large proportion or all of its adhesive power. Furthermore, even after three. hours, some reduction in viscosity and attendant loss of adhesive, power is often evident, particularly in formulations giving an especiallyhigh alkalinity' or where the water used in making the glue is warmer than the normal F. to F. This. rapid deterioration of" s oylcie'ri v glues has; always been a troublesome problem'in; the plye wood industry since it compels close correlation between glue making and glue application along with careful planning to make'sure that substantially' all of the glue will" be consumed before deterioration has occurred and especially when the end of the days run is reached. Also, as noted, there isconsiderable damage from sub standard adhesion from the use of glue which has deteriorated.

Thus, it has always hitherto been considered especially important to mix the glue with either cold water or water that "is not Warmer than normal room temperature and that: any use of heat above room temperature is detrimental and likely" tocause short glue life its attendant d-ifiicul'ties;

It has now been discovered that, notwithstanding thislongestablished belief" that heat should be avoided in mixing soybean glues, actually the use of heat under proper control'is beneficial and, instead of shortening glue life, actually greatly prolongs-it, provided heat of the proper intensity and duration is applied in the early stageof the glue making after the" soybean ma terial has been mixed up as a suspension in water but before dispersion by the addition of any of the strongly alkaline reagents.

The invention therefore comprises the process and product of the step of initially he'ating'ari aqueoussuspension of a soybean glue base in theabsence of strongly alkaline chemicals for a periodofbetween about 3 and Bilminutes to e temperature in the range between about F. and 212F. followed by the addition'of the cus tomary reagents, whereby the finishedglue'. ac quires greatly increased stability and'fresistance to spontaneous decomposition and loss. of ad; hesive power; L Y

The following example illustratesa'preferred embodiment. of the invention: but. is ot'to be construed inv a limiting sense since various mod-iafications. which donot depart from the spiritof the invention, will be; apparent to; gluechemists.

observed.

by the usual dispersing reagents added successively. These are: 12 pounds of hydrated lime previously suspended in 24 pounds of water, 8 pounds sodium hydroxide previously dissolved in 8 pounds water, pounds of N Brand sodium silicate, and finally 2.5 pounds of a mixture of 1.9 pounds of carbon bisulfide dissolved in 0.6 pound carbon tetrachloride, which is added to enhance the water resistance. glue is continued for about 7 minutes whereupon it is ready for use. The resulting dispersed adhesive has an initial MacMichael viscosity of about on the No. 26 wire.

When compared to a similar adhesive made with the same ingredients but with the initial and secondary water added at room'temperature (about F.), this new adhesive shows the following difierences. The adhesive made With room temperature water has an initial viscosity of about 25 on the No. 26 wire which slowly rises to a peak of about at the end of four hours and then slowly diminishes and, after 24 hours, the adhesive has become thinned to a viscosity of about 10 or less, and has developed a strong odor of ammonia. The adhesive made with hot Water also has a slowly rising viscosity curve and reaches a maximum of about 125 at the end of 8 hours with no ammoniacal odor. After standingovernight, it has thinned only slightly and has a viscosity of with only a very slight odor of ammonia. Adhesion tests by making both cold and hot press plywood test panels with both adhesives at various ages show that the adhesive made in the usual way with cold water begins to show noticeable diminution in adhesive power at the end of about 3 hours with a rapid loss of adhesive properties thereafter and, at the end of an over- 1 nightperiod, the adhesive power is entirely lost.

The adhesive made as described above with hot water shows adhesive power fully equal to or slightly'better than that of the adhesive made withcold water and it is maintained for '7 hours. Thereis only a very gradual diminution of adhesive strength thereafter and, even when 24 hours old when a slight odor of ammonia is present, the glue is still thick and spreadable and the adhesion is still of borderline commercial character. V i

The long retention of commercial adhesive power is a new feature not hitherto obtained in soybean glues and particularly the retention of any adhesive power whatever after the odor of ammonia has become detectible is an exception to all previous experience with soybean lues which hitherto have been found to be completely spoiled whenever decomposition has proceeded to the point where the odor of ammonia can be In regard to the heating procedure and its limitations: it has been found that the remarkable extension of glue life may be obtained by various equivalent heating methods A heat treatment at about F. appears to be about the minimum which produces an important extension 'of glue life. At this low temperature, heat treatment for about 30 minutes is' desirable. If the heat treatment is obtained as in the foregoing Stirring of the- 4 example by prom tly stirring the soybean glue base into water which is close to the boiling point, then the maximum effect may be obtained in as short a time as 3 minutes. Various other methods of applying the heat treatment may, of course, be substituted. For instance, if the glue mixer is providedwith a jacket adapted for heating and cooling, the initial'water may be added at room temperature and the heat treatment obtained by running steam through the jacket of the mixer during the initial stirring with restricted water which is customary for the elimination of lumps, followed by coolin to room temperature obtained-by circulating cold water through the jacket at the-end of the heating period.

It has been found to be essential to avoid any substantial heat treatment of the material after the addition of any of the strongly alkaline reagents. If any of these reagents, such as bydrated lime, caustic soda, or sodium silicate, is added while the mixture is very much above room temperature, the chemical activity ofsuch powerful alkaline reagents is naturally greatly enhanced and there is serious danger of alkaline hydrolysis of the protein with resulting loss of adhesive power. However, this-restriction does not apply to the presence of small amounts of soda salts producing only a mild alkalinity or of foam depressants such as pine oil which are fre quently incorporated in the dryglue-base'. The pl-I of the final glue is always well above pH 11.5.

In making, glues according to the present invention, the soybean glue basemay be used either in the form of meal or -flour of various degrees of fineness. Crude extracted soybean meal may be used. If the glue base contains large coarse particles, as in the casefof crude extracted soybean meal, the amount of water required to ob tain a final glue of thesame viscosity will be somewhat increased but the same stabilizing effeet from the heattreatment is obtained. ,The

However, sincethese proteinsare thickened or I even irreversibly-"ooagulated by extended heatmg, ..their presence."ispermissible in only small amounts and the heating must be shortened and restricted to avoid excessive-thickening and increased water requirement. For this reason, the application'of theinvention is most advantageous with the widely used straight soybean flour glues.

It is a remarkable feature of the present invention that the stabilizing effect of the initial heat treatment of thesoybean glue base is always secured regardless of any variations in the reagent formulation used for subsequent conversion of the initial aqueous "suspensiontothe final dispersed adhesive.- Ihgall cases,'the useful extension. of glue life,- resi-stance to decomposition, and delayed appearance of ammoniacal odor are ob tained. The full adhesive power isretained for at least 6 hours'and there is no 'ammoniacal odor during that period. In fact, as indicated p-revimixed with the original dry glue base. The amount of such premixed salts is always very small and their presence does not produce enough alkalinity during the heat treatment to cause any objectionable changes during the heat treatment.

The three strongly alkaline dispersing agents, viz: hydrated lime, caustic soda and sodium silicate-all three of which are always used in soybean glue formulations, are varied somewhat both in amount and order of mixing in various formulations. None of these variations have any adverse eifect on the desirable result from the heat treatment. In some formulae, carbon bisulfide, Which is normally used to enhance water-resistance, is omitted but its presence or absence is also without eflect as far as the extension of glue life due to the heat treatment is concerned.

While no positive explanation can be advanced for the favorable effects of the heat treatment, it appears to have caused some fundamental modification or regrouping of the reactive radicals in the soybean material which, on the one hand, does not have any appreciable effect on the dispersibility or adhesive character but does greatly retard breakdown of the protein. It also seems evident that this change especially retards breakdown of the nitrogenous radicals since, in the heat treated glue, the development of an ammoniacal odor is observed only after very long standing and even then considerable adhesive property is retained.

I claim:

1. In a process of making an aqueous alkaline soybean glue the improvement which consists in mixing a soybean glue base with water to a, stirrable consistency in the absence of acidic and strong alkaline reagents and simultaneously stirring the mixture and heat treating it at the range between about 120 F. and 210 F., for between about 3 and 30' minutes, then cooling the mixture to a temperature substantially not in excess of room temperature and adding to the cooled mixture alkaline reagents to form a glue of spreadable consistency.

2. In a process of making an aqueous alkaline soybean glue the improvement which consists in mixing a soybean glue base with water to a stirrable consistency in the absence of acidic and alkaline reagents and simultaneously stirring the mixture and heat treating it at the range between about 30 minutes at F. and 3 to 5 minutes at 210 F., then cooling the mixture to a temperature substantially not in excess of room temperature and adding to the cooled mixture alkaline reagents to form a glue of spreadable consistency.

3. A glue having a pH of at least 11.5 and a MacMichael No. 26 wire viscosity in the range between about 25 and prepared in accordance with the process of claim 2 and being characterized by the new property of having a slightly ascending viscosity with retention of substantially full adhesive power for a period of at least 6 hours after making with the further feature that during the 6 hour life there is no development of an ammoniacal odor.

4. In a process of making an aqueous alkaline soybean glue the improvement which consists in the step of initially mixing soybean flour to a stirrable consistency with water in the absence of acids and strong alkalies while subjecting the aqueous suspension to heat treatment in the range between about 30 minutes at 120 F. and 3 to 5 minutes at 210 F., then cooling the suspension to a temperature not in excess of room temperature and adding to the cooled suspension strongly alkaline reagents to produce the final adhesive having a pH of at least 11.5 and a MacMichael No. 26 wire viscosity in the range between about 25 and 150.

ALEXANDER J. GOLICK.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS G ea B ta n mm: S p 923 

1. IN A PROCESS OF MAKING AN AQUEOUS ALKALINE SOYBEAN GLUE THE IMPROVEMENT WHICH CONSISTS IN MIXING A SOYBEAN GLUE BASE WITH WATER TO A STIRRABLE CONSISTENCY IN THE ABSENCE OF ACIDIC AND STRONG ALKALINE REAGENTS AND SIMULTANEOUSLY STIRRING THE MIXTURE AND HEAT TREATING IT AT THE RANGE BETWEEN ABOUT 120* F. AND 210* F., FOR BETWEEN ABOUT 3 AND 30 MINUTES, THEN COOLING THE MIXTURE TO A TEMPERATURE SUBSTANTIALLY NOT IN EXCESS OF ROOM TEMPERATURE AND ADDING TO THE COOLED MIXTURE ALKALINE REAGENTS TO FORM A GLUE OF SPREADABLE CONSISTENCY. 